In typical oil and gas well drilling, a drill bit is secured to the lower end of a drill string and lowered into the well. The drill bit is rotated by the drill string, by a downhole drilling fluid motor, or both. The operator pumps drilling fluid down the drill string, which passes through nozzles in the drill bit and flows back up an annulus surrounding the drill string.
In some earth formations, horizontal wells are drilled. The well has a vertical portion that forms a gradual bend with a horizontal portion. Earth formation cuttings tend to build up in certain parts of a horizontal well. The build up of cuttings slows the rate of penetration of the drift bit. Also, the build up can cause the drill string to become stuck.
Surfactants are used in oil and gas well production operations for various purposes. Some surfactants will foam when mixed with well fluid. However, foaming type surfactants are not generally pumped along with the drilling fluid because the foaming would occur within the drill pipe and render the pumping more difficult.